Fuel efficiency and energy efficiency requirements for passenger vehicles are becoming increasingly more stringent. New legislation in the United States and European Union within the past few years has set fuel economy and emissions targets not readily achievable with today's vehicle and lubricant technology.
Over the last decade, the global trend toward tighter carbon dioxide emission regulations has resulted in automobile manufacturers requiring higher levels of fuel economy performance for engine oils. One of the changes car makers are imposing is a slow but steady shift toward lower viscosity grade engine oils such as SAE 0W-20 and SAE 0W-16. Despite this trend, SAE 5W-20, 5W-30, and 10W-30 oils are still key viscosity grades used by many autobuilders and widely sold in the marketplace. Therefore, strategies to improve fuel economy for “5W” and 10W viscosity grade engine oils are of paramount importance to meet tightening fuel economy requirements of new engine oil specifications.
To address these increasing standards, automotive original equipment manufacturers are demanding better fuel economy as a lubricant-related performance characteristic, while maintaining deposit control requirements. One well known way to increase fuel economy is to decrease the viscosity of the lubricating oil. However, this approach is now reaching the limits of current equipment capabilities and specifications. At a given viscosity, it is well known that adding organic or organo-metallic friction modifiers reduces the surface friction of the lubricating oil and allows for better fuel economy. However these additives often bring with them detrimental effects such as increased deposit formation, seals impacts, or they out-compete the antiwear components for limited surface sites, thereby not allowing the formation of an antiwear film, causing increased wear.
Contemporary lubricants such as engine oils use mixtures of additives such as dispersants, detergents, inhibitors, viscosity index improvers and the like to provide engine cleanliness and durability under a wide range of performance conditions of temperature, pressure, and lubricant service life.
Lubricant-related performance characteristics such as high temperature deposit control and fuel economy are extremely advantageous attributes as measured by a variety of bench and engine tests. As indicated above, it is known that adding organic friction modifiers to a lubricant formulation imparts frictional benefits at low temperatures, consequently improving the lubricant fuel economy performance. At high temperatures, however, adding increased levels of organic friction modifier can invite high temperature performance issues. For example, engine deposits are undesirable consequences of high levels of friction modifier in an engine oil formulation at high temperature engine operation.
Improved energy efficiency is of paramount importance to nearly all automobile and equipment manufacturers. Improved fuel economy and energy efficiency can often be achieved by using lower viscosity lubricants or by reducing the kinematic viscosity at 100° C. of the base oil mixture used to formulate an engine oil (Crosthwait et al. “The Effect of High Quality Base Stocks on PCMO Fuel Economy” LW-99-126), however often the higher volatility of such lower viscosity fluids becomes an issue. While there are efforts to develop low viscosity, low volatility base stocks, such fluids will likely produce SAE 5W-30, SAE 5W-20, and SAE 10W-30 oils with very high base oil kinematic viscosity at 100° C. Such oils would struggle to meet industry fuel economy requirements because of a very Newtonian character. SAE 5W-30 and SAE 5W-20 viscosity grades currently represent a large volume of lubricants sold in the United States, therefore low viscosity, low volatility base stocks having improved the fuel economy and energy efficiency of these viscosity grades, without compromising other performance characteristics, are of significant business value.
A major challenge in engine oil formulation is simultaneously achieving high temperature deposit control while also achieving improved fuel economy.
Despite the advances in lubricant oil formulation technology, there exists a need for engine oil lubricants that effectively improve fuel economy while maintaining or improving deposit control.
The present disclosure also provides many additional advantages, which shall become apparent as described below.